Conventional sorting methods
Many particleboard manufacturers producing at an industrial scale rely on a multitude of systems to effectively sort wood — some requiring large-scale investment and vast amounts of space.
Multiple-stage cleaning systems: Multiple-stage cleaning systems are one method to sort the waste wood after it has been collected and cut into smaller pieces. With heights reaching up to 40m, such systems combine numerous techniques working top-down and removing contaminants such as metals, inert material, heavy metals, and many more from the infeed stream. While it is possible to process up to 50 metric tonnes of waste wood per hour, multiple-stage cleaning systems only remove larger impurity fractions. To remove the remaining impurities, operators must often add additional systems such as air separators or optical sorters at the end of the processing line for further purification.
Air separators: Air separators can be used to clean wood chips using blasts of air as materials are transported on a conveyor belt. Lighter wood chips targeted by the airstream continue for processing, while heavier fractions are collected in a separate chamber. Although a vast number of contaminants can be removed with air separators, the level of precision and purity achievable is limited. Impure materials with the same density as wood go undetected, like compound wood materials such as wood chips with nails, coatings, or metallic pieces. For small plants, air separators may be a more favourable option, both economically and due to fewer maintenance requirements.
Water separators: Another solution processors have tried is using water separators based on a sink-float method. Wood chips are fed into a water tank, where the forces of gravity cause lighter fractions to float and heavier materials such as stone, metals and glass to sink. The lighter fractions are then transported by a conveyor belt for further processing. For small-scale production, this is a reliable method that requires simple construction and little maintenance. It is, however, very limited in functionality and performance. Like air separators, the system can only separate light wood fractions and is not capable of sorting processed from non-processed wood materials.